


The Portal // Crossover

by UpFall



Category: Ao no Exorcist | Blue Exorcist, Kuroshitsuji | Black Butler, Tokyo Ghoul
Genre: Blue Exorcist Spoilers, Crossover, Crossover | Toyko Black Exorcist, Demon Okumura Rin, Demon x Demon, M/M, Multi, Season 01 Black Butler, Spoilers, Tokyo Ghoul Spoilers, bxb - Freeform
Language: English
Status: In-Progress
Published: 2019-02-17
Updated: 2019-02-17
Packaged: 2019-10-29 22:43:44
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence, Underage
Chapters: 2
Words: 4,420
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17816912
Author URL: https://archiveofourown.org/users/UpFall/pseuds/UpFall
Summary: It is powerful.It can cross to other dimensions.It is The Portal.





	1. Chapter 1

**Author's Note:**

> The timeline doesn't make sense but let me try to clear it up. It's after Kaneki joined Aogiri Tree, but he's also back at Anteiku. Like I said doesn't make sense, but roll with it.

**March 18th, 2014 / Toyko, Japan.**

"Watch out!"

Kaneki looked up from his book only to get hit straight in the face and knocked onto the pavement.

Ouch, Kaneki thought as he could feel his nose throbbing.

Two younger kids run up to where he lay with scared looks on their faces. Kaneki realized it was the kids that he always saw playing in the playground. He never really acknowledged them so he studied their faces as they approached.

The youngest one looked like a foreigner. Blonde hair mid lengthy curls, blue eyes, a plain white t-shirt, and blue jean shorts. He had a bit of dirt on his face like he fell down not too long ago. 

The eldest one was about eleven or twelve years, also a foreigner. He was a bit more brown, like he spent his days outside alot. Black straight hair going down to his back, green eyes, a touch of freckles wearing a long oversized coat and big boots. Actually, that might be a young girl, whoops.

Kaneki studied them as they got closer and realized they might've just been fighting. Well the girl definitely was, but it looked like the youngest was posted down.

"You idiot! We just got our ball back and now you hit somebody with it?" The older girl scolded the young boy in English, Kaneki realized.

Kaneki stood up wiped, his pants off and grabbed their ball. "Yours?" He said in English and they looked suprised.

"Sorry sir! My brother threw the ball too hard and it accidentally hit you! We are so sorry!" The girl say in perfect Japanese. They both bowed and quickly took the ball.

They were about to run off when Kaneki stopped them. "What happened to your face?"

The girl froze at the question and the young boy looked at her confused as to why she stopped. "N-nothing sir." The girl answered grabbing onto her younger brother.

"What did he ask Eva?" The boy tugged on the girl's jacket. Okay, so only she knew Japanese.

"Did you get into a fight?" Kaneki asked switching to English.

They didn't say anything as Kaneki picked up his book and set it down on the bench he was sitting on. It was a good thing he took that English class with Hide a while back. Oh how he missed hanging out with his best friend.

"Eva! You said we wouldn't get caught!"

"I said we wouldn't get caught by mom not by someone else! Listen next time!" The girl, Eva scowled and turned to face Kaneki obviously to snark him out about minding his own business when her eye caught something interesting which made her confused. He was wearing a medical eye patch and smiling at them.

"What happened to your eye?" She blurted out making Kaneki raise his eyebrows in suprise.

"Hmm, how about this. If i tell you about my eye, will you tell me what happened?" Kaneki asked knowing little kids were always wanting to know things.

"Okay!" They both sat down next to him and the boy wiped his eyes waiting to listen.

"I got into an accident." They both gasped making him chuckle. "My eye... it got infected. So they had to remove it."

It was true, they did remove it. But he got another eye, to be exact a ghoul eye. The kids didn't have to know that though.

"Did it hurt?" The boy asked.

Eva hit her brothers shoulder making him whine about her hitting him. "You're an idiot Wallace! You don't just ask that! What if you had your eye removed and Kai asked you if it hurt? You wouldn't tell him, would you?"

The boy, Wallace shook his head. "But Kai bullies me! If it was you or Mom who asked me, I wouldn't care!"

Kaneki watched as they argued. He could tell they cared a lot for each other but they expressed it through arguing. Kaneki just decided to just let them go. He already knew they got into a fight by piecing it together so he decided to just lecture them.

"You don't have to tell me, but tell your parents." Kaneki said.

"No! Our mom would ground us for life!" Wallace yelled.

_Oh how I wish I took more classes to understand what that meant_ , Kaneki groaned on the inside.

"If you don't, then your mom will find out and be sad you didn't tell her. You don't want your mom to be sad do you?" Kaneki gave them a firm look making their shoulders drop and they shook their heads.

"No, when mom is sad she cries. And that makes Eva cry and then I'm sad! We'll tell mom won't we Eva?" Wallace starts tearing up making his sister sigh.

"Fine." She patted his head. "We'll go tell mom. But I'm telling her!" Eva shouted behind her grabbing the ball and running.

Wallace ran after her. "But you always tell her it was your fault! ... Eva!!"

Kaneki chuckled watching them run off. Kids.

Picking up his book and dusting it off he looked at the sky and realized it was getting dark. Tightening his scarf around him he got ready to head back to the cafe.

 

~

 

Upon reaching Anteiku, the first thing that Kaneki became aware of was the eerie silence. Usually everyone in the cafe was getting ready to lock up, but the thing that made Kaneki pause was that you could usually hear Touka and Nishiki yelling at each other — Touka at Nishiki for not helping and Nishiki at Touka for hitting him for not helping.

He quietly walked up the steps and stood outside the door. Hearing nothing and worried for everyone, Kaneki barged in.

All was still.

The cafe was neatly put away and Kaneki wasn't sure why, but he was chilled to the bone. All the lights were off, chairs straightened, dust cleaned, but nobody was there. 

"Touka?"

Going through the back door he checked all the rooms but no presence was found.

"Irimi? Enji? Hinami?"

He checked the apartments upstairs but still nobody was there. Going to the rooms downstairs, Kaneki knocked on the Manager's door before opening it.

"Manager?"

Kaneki started to freak out.

What if Aogiri tree was back? No, they'd wreck the place. Did the CCG get them? Doubt it, they'd most definitely wreck everything. Was there an emergency he wasn't aware of? But nobody notified him, where was everyone?

Letting his thoughts get ahead of him, Kaneki rushed back downstairs to the cafe but stopped dead in his tracks.

There, in the middle of the cafe was a circle.

"That.. was not there before." Kaneki mumbled to himself inspecting it.

It was a circle with oddly shaped lines and weird colours. But besides that, it looked empty.

Empty in the sense of nothingness. Like a black hole, but it had no gravitational pull. It was like it was supposed to be a portal. All of a sudden his mind went blank. Where was he? Who is he? What is he?

All Kaneki knew was, he had to enter the portal.

And that he did.


	2. Chapter 2

**Notes for the Chapter:**

> I'm going to say this only once, this chapter has spoilers! Well tbh, the whole book is practically a spoiler so don't complain because "you didn't read the note."
> 
> I put Assiah in the beginning because it doesn't exactly say where Blue Exorcist takes place, or if it does I don't know where.

** January 6th, 2010, Assiah. **

"Good morning everyone."

"Morning." Everybody responded as Shiemi skipped into the classroom, well everyone besides one. Rin Okumura.

Rin was too busy holding his head between his palms trying to stay awake. Why was he trying to stay awake? Because he'd been up all night with Ukobach working on a new recipe and before he knew it the sun was up.

"Rin, are you okay? You don't look too good." Shiemi asked looking at the demon with concern.

"He was probably up all night plotting our deaths." Rin heard Bon sneer at him and Rin just rolled his eyes and flipped the guy off.

"Bon, that's kinda uncalled for.."

"Whatever, he deserves it for not helping yesterday." Bon scoffed but Rin was way too tired to argue back. He just nodded and set his head on his desk.

"Usually he argues back, what's wrong with him?" Shima whispered concerned.

"Hell if I care." Bon replied uninterested.

"He doesn't have to argue back!" Shiemi whispered back, defending Rin.

"Shiemi you ask. You're closer to him than us." Izumo jutted her head towards the exhausted Rin making Shiemi's face go red.

"We're not that close..." Shiemi blushed.

Rin, tired of everyone whispering about him, sighed and lifted his head making everyone stop talking and look at him. "Can you guys stop acting like I'm not here."

The door opened making everyone quickly look, but everyone relaxed when they realized it was just Konekomaru coming in. Rin just sighed and rested his head on the desk trying to block out everything.

Konekomaru stopped when he realized all eyes were upon him and he got a confused look in his face. "What? Is there something on my face?"

"No, we just thought you were Sensei." Shima assured him and welcomed him to sit down.

Shima and Konekomaru started talking about yesterday's homework in their other classes which got everybody else back to talking, forgetting they were going to question Rin.

While everyone went back to talking, Shiemi continued to cast a series of glances at Rin in worry. She wondered why he seemed so tired and why he wouldn't of just stay back at his dorm and take a sick day.

Rin, on verge of falling asleep, feels someone's eyes and he tenses up. Then he hears a whisper.

"Rin.. Rin.. are you sure you're okay?"

Too tired to lift his head, Rin just turned it lazily to the voice and noticed Shiemi staring at him.

".....wwhaat?"

"Im asking you if—"

The door opened fiercly making everyone jump and in came Yukio with a stern look. All at once the talking ceased and the group sat up straight, including Rin.

"I hope you all did your assignments, because that's the first thing we'll be going over today." Yukio nonchalantly said as he put his bag down and went to the blackboard.

"Fuck..." Rin mumbled.He totally forgot about it.

Ukobach kept him busy throughout the night with his nagging about how he was ruining their recipe. The more the kitchen demon kept nagging him, the more Rin messed up. By the time they got done with it, the sun was already up and he heard Yukio waking up. Luckily Rin managed to avoid his younger brother this morning, but he forgot one crucial thing: Yukio was his cram school teacher.

Right as Rin cussed himself out for not doing the assignment, both brothers locked eyes. Yukio glared at the eldest, to which Rin casted his eyes downward to avoid suspicion.

Now, Yukio wasn't dumb— as one would expect because he was literally a teacher at 16. But being a teacher at such a young age made him prone to socialization with others his age, he wasn't a teacher for nothing though so he decided to make a certain someone go first.

"Let's start off with Rin."

You could practically hear everyone's groans as they knew their fellow exorcist would've likely forgot. Rin glared at his hands knowing everyone's eyes were upon him.

"Why me?" Rin grumbled looking up to meet his brother's eyes. _Stupid, stupid, four-eyes. Yukio knows exactly what he's doing by sending me first! I don't even know what we were supposed to do!_ He thought.

"No particular reason." Yukio pushed his glasses back up onto the bridge of his nose.

 _No reason my ass!_ Rin mentally screamed.

The two brothers stared at each other, one waiting impatiently and the other mentally stabbing the youngest.

"Ugh, fine.." Rin mumbled and got up to walk to the front of the class. Everyone looked suprised since they were all waiting for him to make up an excuse.

Making eye contact, Shiemi gave an encouraging smile which made Rin's shoulders drop but no more did he relax. He was bluffing and everyone could see it.

Rin was way too tired to think but this assignment was worth way more than to not try. So he brainstormed trying to figure it out. What was the assignment on again? _Something about demons... exorcists.... which chapter are we even on? Last week was about familiars... so we must be on chapter 4... what was chapter 4 about again?... fuck._

"Hurry up shitbrain!" Bon yelled.

"Suguro." Yukio gave Bon a look which got him to shut up. Rin mentally thanked him before he realized it was Yukio's fault he was in this mess so he just glared instead. "We don't have all day, Rin."

"Okay, okay..." The demon nervously licked his lips and glanced around the room noticing what everyone was doing.

Izumo was blowing gum and glaring at everyone and anyone who looked at her, Shima was quietly studying verses, Bon was scoffing at Konekomaru who accidentally dropped his book, Shiemi was feeding her familiar, and wait— where was Takara?

All of a sudden a green hamster and a white-furred dog appeared on the back table making Rin furrow his eyebrows. Mephisto... and of course fucking Amaimon.

"Hey—!" Rin blurted out. Everyone stopped and looked at him and he quickly tried to cover it up. "I mean, uh **cough** hey... so uh my assignment...."

_Looks like you're struggling._

Rin startled hearing a voice rasp in his head. _W-what? Who are you?_

_Guess._

Rin suddenly recognized the voice and he seethed. _Get out of my head Amaimon!_

 _Why?_ The green demon snickered. _It seems like you need help._

"Rin? If you don't present your assignment I'm going to have to—"

"I got it... thanks." Rin yawned as he sharply indicated at his younger brother who just raised an eyebrow gesturing him to start.

 _Sure, like you- out of everyone- a demon would help_. Rin thought but then remembered everyone was waiting for him to start. He started fiddling his thumbs.

_Don't forgot you're also a demon, **little bro**._

_What do you fucking want? I don't have time to entertain you, you fucking sadistic piece of shit._

Rin felt Amaimon's chuckle echo in his brain and he winced. _Demon elements._

 _How is that supposed to.... wait._ Rin paused, he might remember what the assignment was.

"Okay so... we all know the demon, uh elements right?" Rin started off slowly, god he was so fucking tired. He hopes he doesn't mess it up.

"What's your point?" Izumo called out with a smirk. Rin rolled his eyes at her making her glare.

"Well all demons have their own element. Like...." Rin paused making eye contact with Yukio who nodded for him to continue. "Well, like uh, I have fire..... water demons could easily defeat fire demons, like fire could the rot demons."

Rin wasn't sure what to say now. The assignment was actually in reality easy if one were to just study the chapters, but this is Rin were talking about. He wouldn't pick up a book willingly unless it was linked to Satan.

Unbeknownst to the yawning Rin or anyone else, the Earth and Time demons had poofed away from the classroom going back to Mephisto's office.

Heavy lided, Rin tried continuing with his point. "Rotten animal blood attracts goblins which we all know goblins can be small mammals..."

Rin stopped to yawn and that's when his eyes glanced at the back only to see nothing. Confused about where they went Rin frantically searched the classroom with his eyes but to no avail saw only his classmates. Maybe they left because he was talking about Amaimon's kin...

"—the small mammals like mice or hamsters." Rin relaxed, finishing his sentence.

"And what is rotten animal blood made of again? Shiemi?" Yukio suddenly asked making Rin sigh in relief. That gave him a couple more seconds to try and think of what the fuck he was supposed to be going with this.

Shiemi, who was petting her familiar, looked up suprised she was called on and sat up straight with a red face for getting caught not listening. "O-oh uh, rotten animal blood consists of mil..."

The door of the classroom suddenly opened ferociously with a slam against the wall. Half the class jumped at the loud entrance and Shiemi tensed up. Nee noticing his master tense up, hugged the girl who looked like she was on the verge of tears for getting scared. Yukio sighed rubbing his temple whilst looking at the huge dent in the wall the door had just previously impacted. Standing there was Shura in her usual.. scolding attire holding her foot up since she had just kicked opened the door.

"Shura, how many times do I have to—"

"Cut it swordless."

 _Swordless?_ Rin, now alert because of the wake up call, looked at his brother. Yukio was frowning at the name and Rin guessed it was an insult between the two of them.

"I'm here to talk to ye and demon boy."

Rin perked up at that. What did Shura need from him? He was of no use to her.

Yukio nodded and turned towards his class. "I want you all to read up on section #3 and make sure to make notes for your assignment tomorrow. Or if you've already got them, make sure your assignment is complete and use this time to fix any errors. Rin come with me."

Following his brother, Rin was left in thought wondering why he was needed.

Turning out of the room, Shura led the two brothers down a narrow hallway that even Yukio had never seen before. "Mind if I ask what this is all about?"

Shura just glanced at the younger of the two and ignored Yukio's question. She led them down the stairs

Rin nervously flicked his tail back and forth while looking at the floor in anticipation. _Did he do something wrong? Why was Yukio with? Maybe it has to about him instead? But then why am I here if it was about Yukio? Stupid, stupid, stup—_

"We're here."

In front of the two boys stood a huge wooden, oak door. It was in bad shape with scrapes and looked like is was made in ancient Egypt. The floor itself had cobwebs and dust collected on it as of nobody had walked down here in the last five years.

"Here. Here as in... where exactly?" Yukio glanced up, examining the wooden door.

"Go in."

Rin and Yukio glanced at each other and Rin just shrugged not knowing what to do.

"Shura-"

"Go." Shura interrupted crossing her arms looking anything but kidding. Her pink eyes looked dull and she didn't meet their questioning stares.

When none of the brothers moved, Shura's eyes hardened and she reached towards the seal on her chest. Backing up into a fighting stance, Fang was released from her seal and was now in her hands with Shura threatening to block them grom leaving. Just when Shura took out her weapon, Yukio noticed what she was about to do had also took out his pistol and aimed it right as her forehead.

Rin was dumfounded. How did Yukio know she was taking out her weapon? And why was his mentor threatening them. "What the hell Shura?!"

"What are you doing?" Yukio asked calmly, ignoring the outburst of his brother.

"Don't worry your pretty head swordless, I'm not here to kill Rin-" That made Yukio relax a little, but then he tensed up as soon as she continued. "I'm just here ta make sure ye go in."

"Wait what! Why would you kill me!? I thought we were already past that?" Rin yelled accusingly, not taking note of her saying she _wasn't_ about to do anything to him.

"Why is it so important that we go in? What are you planning?" Yukio narrowed his eyes.

"She isn't threatening you if that's what you're asking." A new voice joined in the conversation behind the two boys.

Without turning around Yukio already knew who it was. "Mephisto."

Rin turned around and met the headmaster's eyes. "Mephisto?!"

"Yes, yes. It's me. What's new?" Mephisto joked and walked over to where the all-too-serious Shura stood with Yukio's pistol still aimed at her.

"Then why? And why are you working with him?" Yukio questioned Shura. Everyone knew full well that she hated the demon principal.

"Quite simple, really. You see that door behind you? It's not an ordinary door, as you will soon come to realize." Mephisto smiled and pointed his umbrella at the old door. " ** _Das Tor_** , or as they call it _Iriguchi_."

"An entrance?" Yukio raised an eyebrow.

Rin snorted at how stupid that sounded. "All doors are entrances." He pointed out.

"Ah, but it's **_The Entrance_**. Which entrance? The one, and the only one known to be able to travel between dimensions!" Mephisto held out his arms and grinned.

"Dimensions? What the hell are you talking about? Is this some joke?" Rin butted in yawning a little. Everyone turned to look at the blue demon.

"What does this have to do with us?" Yukio pushed for more information.

"We believe ye two, as the sons of Satan, can open the door. Nobody else is able to." Shura said, keeping her sword Fang still raised.

"Why can't Mephisto?! He's a demon!" Rin huffed putting his hands in his pockets and rocking back and forth on his heels.

 _Not to mention also the son of Satan_. Yukio thought but bit his tongue because Shura didn't know.

"Ah, but I've tried. So have any other demon who can get here. But the most any can do it open it before a light dissipates them." Mephisto chuckled.

"Wouldn't you be dead then?" Rin pointed out not believing the pervy clown.

"I'm the demon of time, I have my ways."

"Why would Shura need to have her weapon out?" Yukio asked, still aiming his pistol as her forehead.

"Just in case. Many unexplainable things have happened to whomever has opened this very door and she's a skilled Exorcist. I've asked her to join us since you're most comfortable around her then any other." Mephisto explained with a glint that nobody but Rin caught in his eye.

"I'm not going through there." Rin growled and went to go back up to steps when Yukio grabbed his elbow.

"I wouldn't do that if I were ye." Shura said as she swiped her sword at Rin.

Rin jumped back right in time, nearly missing the blade. "What the hell, Shura!?" _If it wasn't for Yukio grabbing my elbow I would've been toast._ Rin paled.

"Now, now. No need to be so feisty. All you have to do is, go in. Ah, and one minor thing. It seems that one of your students have successfully made it through the door. You'd like to see is he's okay, am I wrong?" Mephisto grins widely at Yukio to which Yukio switched his pistol to aim at the principal.

"What." Yukio growled at him and gripped the weapon in his hands. Rin started to sweat. He's never seen Yukio like this.

"Mmm, yes. I believe it was... Takara." Mephisto smoothed the crumples on his clothes ignoring the hated glare coming from the young teacher.

"Now, you'll have to make a choice. But you already know that, don't you? Go in and and save your student from wherever they are. Or, stay and protect your brother you promised yourself to never get hurt again, or something along those lines."

Rin glanced at his younger brother, still unaware of the tension in the air. _Why would Yukio need to protect me? If anything as the older one I should be protecting him._

After contemplating for a few good minutes, Shura put her weapon back in her seal. "Well it's up to ye two. I won't force ye to go, but I think Yukio already knows what to do."

 _Won't force?_ Rin snorted eyeing Shura. _What do you call pulling out your weapon and making us try to go through the door then!?_

"Fine. But only for my student. We're not going on some side quest, just there and back." Yukio finally said and put his pistol back.

"There we go! I knew you'd give in! Now, all you gotta do is open the door and walk through the portal—"

"What portal?! You never said anything about a portal!" Rin yelled scowling at his supposed 'brother'.

"That's what he meant by Iriguchi, Rin." Yukio addressed him and turned to face the door. Rin blushed and mumbled, "I knew that.."

The two brothers faced the old, rickety door and Rin nervously licked his lips while swinging his tail. He inhaled and decided to just open it without any thought. Yukio, not expecting him to do that, started yelling at Rin about how he was supposed to be careful, but Rin didn't hear him because he was too entranced with what he saw behind the door.

Once the door opened, Yukio could see why Rin wasn't saying anything and he stopped talking.

There in the doorway was a blue fire mixed with a little bit of gold moving all over the place since it was just exposed oxygen as soon as the door was open. The fire raged and there was electricity surrounding it, sparking in any and every way. It was so intense that the four of them had to step back.

"All you gotta do is walk in." Mephisto whispered into their ears while and gripping their shoulders.

Rin, was too entranced to say anything so he looked at Yukio who met his eyes. With a mutual understanding, both brothers stepped forward and walked into the fire. Nothing happened.

"What?" Rin questioned and looked around only to see Yukio not there. "Yukio?!"

"What a shame." Rin heard someone say. Rin turned towards the voice and saw someone standing next to Mephisto and Shura.

"Takara? What, but Mephisto said..."

Takara grinned, or rather his puppet did. "Hmm yes, but I'm here aren't I? You gotta realize that Yukio has grown quite attached to his students. He'd do anything for one of them. Doesn't that make you feel left out? Your own brother chose his students... over you. Sad." Takara's puppet laughed. Rin growled and went to attack him when the electricity started crackling again.

"Looks like you're about to be reunited with him, tell him I said hi."

"Takara! I'm gonna ki—"

The electricity popped and suddenly Rin was gone. The three left on the stairs just looked at each other and without a word, closed the door and left.


End file.
